1. Field of the Invention
The present invention relates to a light emitting diode capable of directing light emitted therefrom in a predetermined direction, more specifically, to a light emitting diode suitable for use in a back light source for illuminating a liquid crystal displaying panel or the like and a back light unit provided with the light emitting diode.
2. Description of the Prior Art
Conventionally, this kind of light emitting diode includes an element substrate provided with electrodes and wiring patterns, a light emitting element mounted on the element substrate and a sealing body made of a transparent resin material for sealing the light emitting element. The sealing body includes one or more light emitting surfaces having various shapes to emit light from the light emitting element to the outside of the sealing body.
FIG. 7 shows a typical example of a conventional light emitting diode 1 which is composed of a light emitting element 3 mounted on an element substrate 2 and a transparent square sealing body 4 for sealing the light emitting element 3. The element substrate 2 is fixed on a circuit substrate 6.
In order to emit light from the light emitting element 3 through one surface of the sealing body 4, for example, a front light emitting part 4a to the outside of the sealing body 4, both side surfaces 4b and 4c and upper and lower surfaces 4d and 4e of the sealing body 4, except for the front light emitting part 4a are covered by means of light shielding members 5.
The light emitting diode has a side light emitting type in which the front light emitting part 4a has a surface generally perpendicular to a surface 6a of the circuit substrate 6, and light emitted from the front light emitting part 4a is directed in a direction parallel with the surface 6a of the circuit substrate 6, as shown by the arrow in FIG. 7.
FIG. 8 shows an example of a conventional back light unit 11 which is provided with the aforementioned light emitting diode 1. The back light unit 11 is composed of an optical wave-guide 12 mounted on the surface 6a of the circuit substrate 6 and a light source for illuminating the optical wave-guide 12, for example, the light emitting diode 1 of the above type.
One side surface of the optical wave-guide 12 is formed with a light receiving surface 13 and for example, two light emitting diodes 1 are disposed on the surface 6a of the circuit substrate 6 in such a manner that the front light emitting part 4a of each of these light emitting diodes is faced with the light receiving surface 13 of the optical wave-guide 12.
In the back light unit 11, the light emitted from the front light emitting part 4a of the light emitting diode 1 is entered into the light receiving surface 13 to illuminate the optical wave-guide 12.
In this case, it is possible to cause light of a high brightness to enter from the front light emitting part 4a of the light emitting diode 1 into the light receiving surface 13 of the optical wave-guide 12, because the light receiving surface 13 of the optical wave-guide 12 is disposed to face the front light emitting 4a of the light emitting diode 1 and the both side surfaces 4b and 4c and upper and lower surfaces 4d and 4e of the sealing body 4 are coated with the light shielding members 5.
In the conventional light emitting diode 1, because the both side surfaces 4b and 4c and upper and bottom surfaces 4d and 4e of the sealing body 4 except for the front light emitting part 4a are coated with the light shielding members 5, the brightness of light emitted from the front light emitting part 4a can be increased, but, the directivity of light, in other words, a region of scattering the light becomes narrow. Therefore, if the optical wave-guide 12 having a relatively large plane size is illuminated, a plurality of light emitting diodes must be disposed along the light receiving surface 13 of the optical wave-guide 12, as shown in FIG. 8.
However, even though the plurality of light emitting diodes 1 are disposed, because of a narrow scattering region of light from the front light emitting part 4a, there is a problem that regions A (shaded areas in FIG. 8) which are not illuminated by lights are generated between the adjacent light emitting diodes 1 and 1, and at the opposite sides of the optical wave-guide 12, as shown in FIG. 8.
Consequently, the light emitting diodes 1 must be disposed with a narrow space in order to illuminate uniformly the light receiving surface 13 of the optical wave-guide 12. As a result, there is a problem that the number of the light emitting diode 1 becomes large and considerable time and labor are required for an attachment of the light emitting diode 1 and therefore a cost for manufacturing the back light unit 11 becomes high.
If a large number of light emitting diodes 1 are provided, there is a limitation to a space in which the light emitting diodes 1 are disposed, eventually, it is difficult to illuminate uniformly the optical wave-guide 12.